1. Field of the Invention
Marking pen holders with particular reference to markers used in the fitting of spectacles lenses.
2. Discussion of the Prior Art
In the fitting of spectacles lenses, it is necessary to accurately position the lens' optical reference (e.g. optical center) relative to the patient's pupil for optimum lens-eye performance. This requires that the optical center (OC) be so positioned that the lens optical axis passes through the center of rotation (CR) of the eye. For example, for distance viewing the OC's lateral disposition depends upon monocular pupillary distance (PD). The OC's vertical disposition is dependent upon the stop position distance (SPD), i.e. the rear lens vertex to CR distance, and the pantoscopic angle (PA). For normal SPD's, the trigonometric relationship dictates that for each two degrees of PA the OC be decentered down approximately 1 mm from the pupil center (with the eye in its primary gaze posture). For a 10.degree. PA, the OC should be decentered down approximately 5 mm from the pupil center.
Accordingly, in order to satisfy the requisites of optimal fitting, it is necessary to first establish the location of the pupil center projection, i.e. within an empty frame's eyewire (lens rim). One of the practiced techniques entails attaching a clear plastic membrane, e.g. cellophane tape, to each eyewire so that it will encompass the intercept of the pupil center projection. Then, while employing a fixation technique to insure the patient's parallel primary viewing, the pupil centers are marked on the tape. These markings may then be measured using the well-known frame boxing references.
While the foregoing technique may be simple in concept, it is difficult in practice to mark the pupil center accurately. The difficulty arises from prematurely or accidentally touching the surface to be marked as a result of the fitter heretofor having to observe the patient's pupil without the assistance of a hand rest or reference to stabilize or control the marking pen.
These difficulties are circumvented by the present invention which has a principal objective of providing means for stabilizing a marking pen prior to and during marking therewith.
Another object is to provide a pen rest adaptable to pen replacement and having convenient pocket portability.
Still another object is to provide a highly practical and efficient marking pen stabilizer of uniquely simple design and inexpensive construction.
Other objects and advantages of the invention will become apparent from the following description.